Wi-Fi-equipped shuttle buses, which ferry tech employees from San Francisco to their jobs in Silicon Valley, are just one perk offered up by companies like Google, Yahoo, Apple and Facebook. For some locals, these buses have become a tangible symbol representing the aggressive wave of gentrification sweeping through large swathes of San Francisco and Oakland. Now, almost as if in response, the city of San Francisco has outlined plans to tax the tech companies if they want to continue offering their workers private transportation.

On Monday, San Francisco Mayor Ed Lee announced an 18-month pilot program where shuttle companies will be charged based on the number of stops they make in city bus zones, the San Francisco Chronicle reported.

If the program passes (it needs the approval of the city transportation authority, and it looks like it will get it), shuttle operators will need a city permit to continue using public bus stops. At $1 per day per stop, the fees are intentionally low (they are limited by state law to only cover the costs of the pilot program). The mayor's office estimates it will bring in $1.6 million in revenue, all of which will be used to pay for the program.

Other requirements will also go into effect if the program passes: permit holders must yield to city buses, avoid certain streets, and provide ridership and location data for enforcement and program adjustments.

Proponents of the private buses say the buses cut emission levels and congestion, while critics and activists say they are just another example of the technology industry forcing San Francisco to offer up overly generous policies (including large tax breaks for companies like Zynga and Twitter).

San Francisco Supervisor Scott Weiner, whose district includes parts of the Mission -- an increasingly trendy area of San Francisco, where some of the bus protests have taken place -- warned that lashing out against tech workers was not the right approach to address the issue of gentrification. "We need to stop politicizing people's ability to get to work," the San Francisco Chronicle reported Wiener saying at a news conference to announce the pilot program.